Date Full Report Received02/20/2019
Date Abstract Report Received02/20/2019
InvestigationInstitution: Iowa State University
Primary Investigator: Dr. Kenneth J. Stalder Ph.D.
Co-Investigators: Tom Baas, Max Rothschild, Anna Johnson, Joseph Stock, Julia Calderon Diaz
Funded ByNational Pork Board
The development of an objective method to select replacement gilts with the most desirable structural conformation would likely decrease the likelihood of the female to be culled early in life and increase welfare and profitability of the herd overall. The primary goal of this study was the validation of an objective method to evaluate feet and leg structural traits of replacement gilts and to identify the similarities and differences between objective and subjective structural conformation scores. A second goal was to estimate the impact of lysine concentration in gilt development diets on gilt feet and leg conformation. Finally, a third goal was to identify the relationship between objective feet and leg conformation joint angles across different time periods and sow longevity / lifetime productivity to develop guidelines for replacement gilt selection. Maternal line crossbred Large White × Landrace gilts (n = 641) were used in this study. Gilts (n = 72) were moved on a weekly basis for 9 weeks to the gilt development unit at 77 days of age. Within each weekly group, 24 gilts were randomly allotted to one of three pens. The allotted three pens were fed ad libitum diets designed to provide similar ME but to differ in dietary SID lysine levels. At 100 d of age gilts were individually evaluated for feet and leg conformation traits using a subjective and an objective method. A subjective evaluation method for gilt’s conformation traits was used to score knee, hock, front and rear pastern using a 5-point scale where extreme scores represent extreme phenotypes. Additionally, animals received a lameness score based on stance and movement on a 4-point scale from zero to three, where 0 = no observed lameness, 1 = mild lameness, 2 = moderate lameness and 3 = severe lameness. Gilts were individually recorded using video and joint angles for the knee, front and rear pastern, and hock were measured. Subsequent subjective and objective measures were recorded at 200 d, 1st and 2nd weaning for animals that remained between those periods. Productivity traits were additionally recorded for gilt development (i.e. growth, muscle and fat deposition), as well as maternal traits (i.e. reproductive age and success, total born and stayability) for first and second parity.
Goal One: Validation of an objective method to evaluate feet and leg soundness for replacement gilts and to identify the similarities and differences between objective and subjective structural conformation scores: Front and rear pastern joint angles decreased and hock joint angles increased as time progressed. Knee joint angle decreased by 3 degrees from 200 d to the 1st weaning; however, knee joint angle increased 2 degrees by 2nd weaning. Females with greater knee, hock, front and rear pastern joint angles at 100 d of age, continued to have greater joint angles later in life (0.2 ± 0.04 degrees). A majority of gilts received the middle score (i.e. score 3) when joint angles were subjectively evaluated. Joint angles among subjective scores followed logical numerical classification patterns, i.e. joint angles should be lower for lower subjective angle classification. However, no difference in joint angles was observed among the corresponding scores for knee, front pastern and hock, indicating minimal variation existed among the subjective scores. A difference was observed between subjective scores for the rear pastern, where scores of ≤ 2 and 3 were lower than score of ≥ 4 by 4.0 and 3.5 degrees, respectively. No variation was observed between scores ≤ 2 and 3 for the rear pastern, indicating that no significant angular difference existed between the two scores. Twenty-four animals were classified as lame. No significant differences (P ≥ 0.05) in joint angles were observed across all traits between lameness classification statuses. Weight at 200-d was significant (P < 0.05) for the knee measure, where the regression coefficient (-0.03 ± 0.01) indicates that greater weights at 200-d have lower knee joint values (more flexion). Heritability estimates ranged from 0.05 to 0.13 for subjective scores and 0.18 to 0.43 for objective scores. Objective evaluation heritability estimates were greater than subjective score heritability estimates for all comparable traits. Females with greater knee, hock, front and rear pastern joint angles at 100 d of age, continued to have greater joint angles later in life.
Goal Two: To estimate the impact of lysine concentration in gilt development diets on gilt feet and leg conformation: There was no interaction between dietary treatment and evaluation point for any of the feet and leg conformation traits studied. Rear pastern angles for females fed the low and medium SID lysine were, on average, 1.3 degrees greater compared with females fed the high SID lysine diet. There was no difference between dietary treatments for knee joint angles. Hock and front pastern joint angles tended to be greater in females fed the medium SID lysine diet compared with females fed the low and high SID lysine diets.
Goal Three: Identify the relationship between objective feet and leg conformation joint angles across different time periods and sow longevity / lifetime productivity to develop guidelines for replacement gilt selection: Phenotypic correlations between traits were low. Genetic correlations were low to moderate between traits and additionally had large standard errors that indicate potential for correlations that are not different than zero. However, genetic correlations between front pastern angulation and days to 113 kg (-0.59 ± 0.25), knee and front pastern and last rib backfat (-0.44 ± 0.15 and -0.51 ± 0.23, respectively), front and rear pastern angulations and first farrowing total born and born alive, and age at first farrowing and stayability through second farrowing (-0.46) were moderately negative. Front and rear pastern angulation and fat-to-lean ratio (0.50 ± 0.24 and 0.41 ± 0.20, respectively) and rear pastern angulation and stayability through second farrowing (0.45) were moderately positive.
• Measures of feet and leg conformation utilizing the objective measurement methods may exhibit greater variation than those utilizing subjective scores and could be more beneficial in identifying structural differences among animals in a selection program.
• Dietary lysine level had little to no effect on structure across time periods.
• Objective evaluation at selection should indicate joint structure for later time periods, when taking into account the changes in pasterns and hock described in this study.
• Joint changes were similar as observed in previous work and indicate that animal’s feet and leg conformation changes in a favorable direction and minimal if any joint changes between 1st and 2nd weaning indicate that the joint change is localized to a specific time-period.
• Genetic correlations indicate that while animals selected for proper conformation could be fatter, additional total born and born alive piglets in the first parity could be an additional benefit.
For more information, please contact Dr. Kenneth Stalder (email@example.com)